Transient field measurements on light and heavy ions in amorphous iron-boron compounds

Measurements of transient magnetic fields (TF) were performed for the first time in the amorphous compounds of Fe₈₀B₂₀ and Fe₈₅B₁₅ for ²⁴Mg(2⁺), ²⁸Si(2⁺), ⁴⁸Ti(2⁺) and ⁵⁶Fe(2⁺) probe ions employing light and heavy ion beams. The motivation for these experiments was to investigate whether ion beam induced attenuations of TF are substantially weaker in these materials than in crystalline Fe. This expectation was indeed satisfied. The attenuations observed were found to be smaller at least by a factor of 2.     

Quantitative Imaging by Optical Diffraction Tomography

Optical diffraction tomography (ODT) is applied to reconstruct the cross-sectional, complex refractive index distribution of cylindrical objects. Experimental reconstructions showing noticeable image contrast for refractive index variations of about 0.001, and having a spatial resolution of about 2 μm, are obtained for objects with cross-sectional diameters of about 100 μm. The results demonstrate that ODT can be used for quantitative imaging of semitransparent fibers.Presented at the International Commission of Optics Topical Meeting, Kyoto, 1994.     

Focusing of electromagnetic waves into a uniaxial crystal

We derive integral representations suitable for studying the focusing of electromagnetic waves through a plane interface into a uniaxial crystal. To that end we start from existing exact solutions for the transmitted fields due to an arbitrary three-dimensional (3D) wave that is incident upon a plane interface separating two uniaxial crystals with arbitrary orientation of the optical axis in each medium. Then we specialize to the case in which the medium of the incident wave is isotropic and derive explicit expressions for the dyadic Green's functions associated with the transmitted fields as well as integral representations suitable for asymptotic analysis and efficient numerical evaluation. Relevant integral representations for focused 3D electromagnetic waves are also given. Next we consider the special case in which (i) the incident field is a two-dimensional (2D) TM wave and (ii) the optical axis in the crystal lies in the plane of incidence, implying that we have a 2D vectorial problem, and derive dyadic Green's functions, integral representations suitable for asymptotic and numerical treatment, and integral representations for focused TM fields. Numerical results for focused 2D TM fields based on these integral representations as well as corresponding experimental results will be presented in forthcoming papers.     

Synthetic strategies to prepare 2-alkyl, 2-aryl and 2-acetylenyl substituted 4,6-diamino-1,3,5-triazines

We have developed synthetic protocols to generate 2-alkyl, 2-aryl and 2-acetylenyl substituted 4,6-diamino-1,3,5-triazines from the corresponding 2-chloro compound.     

Generalized nuclearity conditions and the split property in quantum field theory

Generalized nuclearity conditions that are applicable in arbitrary superselection sectors of a quantum field theory and to theories with a maximal temperature are discussed. They are shown to imply the (distal) split property and to impose specific restrictions on the spectral properties of modular operators associated with local algebras and vectors of compact energy support.     

Electronic Absorption Spectra of Planar,Conjugated Biradicals in the Lowest Triplet State

The semiempirical PPP-SCF-SCI method has been adapted to even-electron, open-shell π-systems by performing the SCF calculation on the lowest triplet configuration and choosing a limited set of single electronic excitations from the latter for configuration interaction. The basic approximations and parameters of the standard PPP model were retained. The results were compared with experimental triplet-triplet absorption spectra of aromatic hydrocarbons and with more elaborate calculations available for selected systems. The reliability of the model was found to be comparable to its well-known performance in predicting the absorption spectra of closed-shell π-systems and of conjugated radicals. Triplet-state absorption spectra for various planar, conjugated biradicals were calculated and, where possible, compared with experimental data.     

Complete enantiospecificity in the highly regioselective and stereoselective photo- and thermal rearrangements of some homoconjugated ketones

The oxa-di-π-methane (ODPM) photorearrangement of 2-(carbomethoxy)spiro [5.5]undeca-1,3-diene-7-one ($\text{1}$d) to $\text{2}$d and the latter's thermal rearrangement to $\text{3}$d were shown to be not only fully regio-and stereoselective but also to occur with complete enantiospecificity. An additional example, the 2-hydroxymethyl derivative ($\text{1}$f) was also studied and the two systems were chemically correlated.